Alexander the Great was clearly insane, even by the cultural standards of his time. According to Diodorus, a month before he mercifully died (or, more likely, was assassinated) his own generals invited Babylonian priests to exorcise the demons that may have possessed him. Plutarch calls him "disturbed". He describes extreme mood swings that today would require medication to quell and control. The authoritative Encyclopedia Britannica attributes to him "megalomania and emotional instability". It says:

"He was swift in anger, and under the strain of his long campaigns this side of his character grew more pronounced. Ruthless and self-willed, he had increasing recourse to terror, showing no hesitation in eliminating men whom he had ceased to trust, either with or without the pretense of a fair trial. Years after his death, Cassander, son of Antipater, a regent of the Macedonian Empire under Alexander, could not pass his statue at Delphi without shuddering."